In this article I reconstruct the contribution of some central Hellenistic political thinkers to a theory of human rights. Starting point is the traditional Stoic conception of the law of nature as a power in which only perfect human beings actively participate. In the 2^nd century BC the Stoic Panaetius adjusted this traditional high-minded theory by also allowing for a lower level of human excellence. This second-rate human excellence can be achieved just by following ‘proper functions’, which are derived from ordinary human nature and can be laid down in rules. From here, it was only a small, yet decisive step – presumably to be attributed to one of Cicero’s teachers – to discard the highest level of human perfection altogether. This step, I argue, paved the way for an understanding of the rules of natural law in terms of human rights.